1. Field of the Invention
The present invention relates to a method for retarding the staling of baked goods, and more particularly to a method for achieving the thermal protection and sustained release of a certain enzyme throughout a baked good during and following the baking process.
2. Description of the State of Art
The phenomenon of bread staling has been studied extensively and a variety of theories have been presented. It is now generally accepted that staling is due to a gradual transition of starch from an amorphous structure to a partially crystalline state. This increase in starch crystallinity, also referred to as retrogradation, is caused by an intermolecular or intramolecular association via hydrogen bonding of the two polysaccharides, amylose and amylopectin, which comprise starch granules.
Amylose is made up largely of unbranched chains of D-glucose units (100-1,400 units) which are joined together by alpha-(1,4)-glucosidic bonds. Retrogradation of amylose is rapid due to the ease of alignment of the linear molecules. Amylopectin is the main constituent of starch and, like amylose, it is also constructed from D-glucose units, but in the case of amylopectin they are assembled in shorter, rather bush like, branched chains, containing only 20-25 units of D-glucose. The links in the chain are alpha-(1,4)-glucoside bonds, while the branching points involve alpha-(1,6)-glucosidic bonds. The branched structure of amylopectin interferes with molecular alignment, and consequently amylopectin retrogradation occurs at a much slower rate.
During baking, starch granules swell and absorb moisture, but gelatinization is not complete because of limited water availability. As the granules swell, amylose and to a lesser extent amylopectin diffuse from the granules into the interstitial volume. The solubilized linear molecules retrograde rapidly and form a crystalline network which in combination with the gluten matrix form the characteristic xe2x80x9ccrumb setxe2x80x9d or structure of bread and other baked goods.
Staling of baked goods is generally defined as an increase in crumb firmness and a corresponding loss in product freshness. Flavor, aroma, texture, perceived moisture level, and other product characteristics are also negatively affected as staling proceeds. The staling process begins as soon as baking is complete. Amylopectin remains mostly in the starch granule and retrogrades slowly during product storage. Retrogradation occurs by intermolecular and intramolecular association of linear segments, and to a lesser extent between amylopectin and amylose at the interface of the starch granules and the interstitial volume. As amylopectin retrogradation proceeds, a three-dimensional crystalline structure is formed slowly, causing an increase in firmness, or staling.
Factors that control the rate of staling include time, temperature, moisture level, and the presence of additives such as emulsifiers (crumb softeners). Rate of staling shows a linear response with time, but can be minimized by maintaining the maximum allowable moisture in the product or by storage at warm (room temperature or higher) or cold (below freezing) temperatures. Refrigeration enhances staling since the rate of retrogradation is optimal at cold temperatures just above freezing.
Staling eventually causes a product to become unacceptable at the retail or consumer level. It is estimated that 3-5% of all baked goods produced in the United States are discarded due to a loss in freshness. The value of discarded baked goods has been estimated to exceed $1 billion annually in the U.S. alone. It is obvious that prolonging the freshness of baked goods by retarding staling would be a benefit to the producer, retailer, and consumer.
A common practice within the baking industry to retard staling is to add chemical emulsifiers to the dough formulation. About 12-15 million pounds of distilled monoglyceride and 20-25 million pounds of mono- and diglycerides are used annually in the baking industry for this purpose. However, while chemical emulsifiers do produce a softer bread, they are only partially effective in reducing bread staling because they appear to function by creating softer bread out of the oven rather than by acting upon the mechanism of starch retrogradation directly. That is, the bread still stales at about the same rate, but it starts from a softer loaf and so reaches unacceptable firmness later than untreated bread. As can be surmised from this description, a limiting factor in surfactant use is the initial softness of the loaf: both bakery production processes (such as slicing), and consumer preferences require a certain level of firmness in bread which sets a limit to surfactant use.
In addition to the usage of chemical emulsifiers, enzymes which modify the starch responsible for staling are also used for increasing shelf-life of baked goods. Enzymatic techniques for reducing firming in baked goods have been studied for years, and the beneficial action of enzymes has been recognized. However, commercially available enzymes have been in the past either only marginally effective or they produced offsetting negative effects in product quality that precluded widespread use.
The amylases are a specific type of enzyme which hydrolyze the glycosidic linkages in polyglucans, and for this reason are grouped with hydrolases. The specific amylases of special interest to bakers are alpha-(1,4)-glucan glucanohydrolase (or alpha-amylase) and alpha-(1,4)-glucan maltohydrolase (or beta-amylase) derived from various cereal and microbial sources. The amylases are widely distributed in nature, occurring in many animal tissues, higher plants, molds, yeast and bacteria. Until recently, the only alpha-amylases used in baking were cereal enzymes from barley malt, fungal enzymes derived mainly from Aspergillus oryzae, and bacterial enzymes derived from Bacillus subtilis. Depending on their origin, alpha-amylases show measurable differences in certain properties, such as pH and temperature optima, thermostability, and resistance to inactivation by acidity. They are simple crystallizable proteins that do not require the presence of coenzymes for their activity. Because of their protein nature, they exhibit a general heat lability. Table 1, shown below, demonstrates the thermostability of alpha-amylases from various sources.
The data in Table 1 demonstrates that fungal alpha-amylase is quite heat labile and is inactivated rapidly at temperatures above 149xc2x0 F. (65xc2x0 C.). A temperature above 167xc2x0 F. (75xc2x0 C.) is required for a comparable inactivation of cereal alpha-amylase. Bacterial alpha-amylase is the most stable and shows little loss of activity at temperatures up to 185xc2x0 F. (85xc2x0 C.).
As the temperature of the dough rises during baking, starch is gelatinized over the range of 140xc2x0 to 167xc2x0 F. (60xc2x0 to 75xc2x0 C.), rendering it susceptible to amylase attack. Alpha-amylase specifically hydrolyzes the alpha-(1,4)-glycosidic linkages in starch at random points within the amylose and amylopectin molecules. Some alpha-amylases are capable of hydrolyzing linkages within the amorphous regions of the starch matrix during baking. Under the proper conditions, this limited degree of hydrolysis is sufficient to disrupt the starch network and reduce the rate of staling.
Barley malt is often added directly to wheat flour at the mill to standardize alpha-amylase activity. Standardization enhances production of fermentable sugars from damaged starch, increases yeast growth and gas production, and improves dough handling and proofing. Barley malt also improves finished product properties such as color, grain, texture, and flavor. However, since barley malt retains much of its activity over the temperature range of starch gelatinization, it is important to avoid an excess of cereal amylase to prevent the undesireable result of gummy, sticky crumb. Shelf-life, however is not improved.
Bacterial alpha-amylase enzyme most often refers to enzymes made from Bacillus subtilis, and are able to inhibit staling by hydrolysing glycosidic linkages within the amorphous areas of gelatinized starch. The enzyme is most active at a pH of about 7 and a temperature of about 75 to 80xc2x0 C.
One enzymatic approach to retarding bread staling is disclosed in U.S. Pat. No. 2,615,810 to Stone and involves the use of a heat-stable bacterial alpha-amylase enzyme to attack gelatinized starch granules during baking. A refinement to Stone""s approach is described in U.S. Pat. No. 4,299,848 to DeStefanis, et al. which discloses a process for the inactivation of the proteolytic enzymes present in commercially available heat stable bacterial alpha-amylase enzyme preparations obtained from extracts of Bacillus subtilis, Bacillus stearothermophilus or other microbial sources. In a further refinement, U.S. Pat. No. 4,654,216 to Carroll, et al. discloses the addition of an enzyme mixture of heat stable bacterial alpha-amylase and a pullulanase to dough in proportions of from 0.25 to 5 SKB (alpha-amylase units) and 5 to 75 PUN (debranching enzyme units) per 100 grams of flour.
G. Bussiere, et al. in xe2x80x9cThe Utilization of Alpha-Amylase and Glucoamylase in Industrial Baking Technology,xe2x80x9d Annales De Technologie Agricole,vol. 23 (2), pp. 175-189 (1974) disclose studies on the role of heat stable bacterial alpha-amylases derived from Bacillus subtilis in bread making technology. Bussiere, et al. teach that heat stable alpha-amylases of bacterial origin are effective in retarding staling, but produce a sticky bakery product when a dosage of 2.5 SKB units or more per 100 grams of flour is used.
A drawback of the Stone, DeStefanis, et al., Carroll, et al., and Bussiere, et al. approaches is the tendency of heat stable bacterial alpha-amylases to remain active too long during baking and to cause gumminess in the finished product. As a result, these approaches require a degree of control over dosages and enzyme ratios which may be impractical to apply commercially.
Further attempts to improve the action of bacterial amylases have focused on genetic manipulation of the naturally occurring bacteria to create a bacteria which produces alpha-amylase which is less thermostable. Some of these products, such as Novamyl(copyright) from Novo Nordisk BioChem (Franklinton, N.C.) have partially overcome the limitations of naturally occurring bacterial amylase and have achieved some acceptance in the industry, but finished product quality still needs improvement and the reliance on genetic modification makes such products unacceptable for use in xe2x80x9cCertified Organicxe2x80x9d foods (as defined by the California Organic Foods Act of 1990) which constitutes a significant developing market for baked goods.
Fungal alpha-amylase enzymes are effective in partially hydrolysing damaged starch and are often added to flour, in the same manner as barley malt, to develop desirable properties for baking. However, conventional fungal amylases exhibit limited thermostability and are, for the most part, inactivated prior to the onset of starch gelatinization during baking since their optimum temperature range is only 50-55xc2x0 C. As a result, fungal alpha-amylases have little effect on amylopectin hydrolysis and do not exhibit significant anti-staling activity.
In an attempt to provide a fungal alpha-amylase that exhibits anti-staling activity, Cole in his U.S. Pat. No. 4,320,131 discloses that the thermal stability of fungal alpha-amylase is substantially increased by dispersing aqueous solutions of the enzyme in concentrated sugar solutions. This procedure reportedly protects the enzyme from thermal denaturation, allowing it to retain activity during baking. Use of the stabilized enzyme in conjunction with the proper emulsifier in a carefully controlled process reputedly reduces product firmness, although use of the enzyme alone is not effective. However, the processing and ingredient changes required make this approach unsuitable for a number of bakery applications.
Livermore, et al., in PCT Application WO 98/32336, disclose a latent enzyme preparation for use as a bread improver to improve the quality of a loaf of bread. The latent enzyme is prepared by coating a microparticulate form of alpha-amylase with a fat having a slip melting point of at least 35xc2x0 C. According to the method of Livermore et al., the required level of encapsulation of the enzyme with the fat is less than 100%, and in some cases is less than 50%. Due to the choice of fat used by Livermore et al. to coat the enzyme, the enzyme is released into the dough during the proofing stage of the bread making process. That is, active, unprotected enzyme is release into the dough during the proving stage and early in the baking process. It is known that fungal alpha-amylase becomes heat-denatured at temperatures around 50xc2x0 C. Therefore, since the alpha-amylase in the Livermore et al. preparation is no longer coated by the fat once the dough enters the baking stage, the alpha-amylase is consequently denatured during the baking stage, which is typically done at temperatures much higher than 50xc2x0 C. As a result, the baked good produced by the method of Livermore et al. does not contain an active enzyme.
There is still a need, therefore, for a method and composition produced therefrom which utilizes alpha-amylase enzymes in a manner that is suitable in a number of bakery applications and which achieves an acceptable baked good having an extended shelf-life.
Accordingly, the present invention provides a method for retarding the staling of baked goods and for extending the shelf life of baked goods.
More specifically, this invention provides a delivery vehicle for alpha-amylase enzymes which protect the enzyme from thermal denaturation and provides for a sustained release of the enzyme.
This invention further provides a delivery vehicle containing an active alpha-amylase enzyme for combining with ingredients for the preparation of a baked good, wherein the delivery vehical releases active alpha-amylase enzyme into the baked good to reduce the staling rate of the baked good.
This invention further provides a baked good having incorporated within it a delivery vehicle which continuously releases an active alpha-amylase enzyme during the baking process and in the baked good.
The baked goods of this invention and the methods provided for preparing such baked goods meet the requirements of the California Organic Foods Act of 1990 or any comparable act.
Additional objects, advantages and novel features of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities, combinations, and methods particularly pointed out in the appended claims.
To achieve the foregoing and other objects and in accordance with the purposes of the present invention, as embodied and broadly described therein, the method of this invention results in a baked good comprising flour, water, other dough-forming ingredients, and an effective quantity of a loaded delivery vehicle to enhance the shelf-life of the baked good, wherein the loaded delivery vehicle comprises alpha-amylase particles encapsulated with a food grade lipid.